摘要:

Abstract35Cl NQR spectra of substituted phenylisoxazoles and isoxazolines were analysed. For certain molecules the atom charges and orbital populations were calculated with the MINDO/3 method. It was proved that a chlorine atom at position 4 on an isoxazole ring transmits the influence from the phenyl ring at position 3 to the phenyl ring at position 5 on the isoxazole ring through the system of π‐bon

ISSN:0749-1581    

DOI:10.1002/mrc.1260321002

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractOne‐bond deuterium‐induced isotope shifts of13C NMR (1Δ) for 106 sp2‐hybridized carbons are discussed in terms of CH bond lengths.1Δ correlates linearly with the related CH bond length calculated by the MNDO MO method by the equation1Δ(ppb)=8350rC

ISSN:0749-1581    

DOI:10.1002/mrc.1260321003

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe total proton and carbon‐13 NMR assignments of quinghaosu I, II and V isolated fromArtemisia annuacultivated in Brazil and of the synthetic derivatives quinghaosu alkene, ketone and epoxy are reported. The conformations and conformational equilibria of these compounds in solution were obtained from the spectral data and molecular mechanics calculation

ISSN:0749-1581    

DOI:10.1002/mrc.1260321004

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractThe29Si and13C NMR chemical shifts are reported for trimethylsilyl derivatives of 25 amino acids, the majority of which occur naturally as protein constituents of foodstuffs. The29Si chemical shifts in trimethylsilyl esters of amino acids roughly correlate linearly with the pKvalues of the parent amino acid. No such simple correlations were found for the shifts in the fully trimethylsilylated amino acids. The29Si chemical shifts of various functionalities encountered fall into distinct spectral regions, but the shifts of (CH3)3SiN or (CH3)3SiOOC groups alone are not sufficiently characteristic to identify the acid but their combination is in most cases.

ISSN:0749-1581    

DOI:10.1002/mrc.1260321005

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractBy means of the IGLO method the31P NMR chemical shift, δiso, the principal values, σii, and the orientation of the principal axes of the shielding tensor were calculated for a number of dithiadiphosphetanes [RP(S)S]2and of dithioxophosphoranes RPS2with RH, CH3or C6H5. The calculated compare well to the available experimental data from solid‐state NMR and can be taken as predictions where no experimental data are available. The dependence of the principal values σiion geometry changes and the substitution was studied. The shielding tensors were calculated as sums of contributions of localized molecular orbitals. These contributions were used to discuss the effects observed. They provide valuable insights into relationships between geometrical structure and the principal value

ISSN:0749-1581    

DOI:10.1002/mrc.1260321006

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractCarbon‐13 and proton resonance assignments for a DNA fragment complexed with its regulatory protein were obtain with the use of a selectively13C‐labelled oligonucleotide. Data obtained on the Lac operator–Lac repressor complex from the HMQC–NOESY maps of the free and complexed Lac operator demonstrate that only minor conformational modifications are induced on compl

ISSN:0749-1581    

DOI:10.1002/mrc.1260321007

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractNatural abundance17O NMR spectroscopic data, in toluene‐d8at 90°C, were obtained for different classes of steroids, including androstanes, estranes, pregnanes, cholanes and cholestanes. Only routine acquisition parameters were used in combination with linear prediction methods during the processing for eliminating acoustic ringing artifacts. The results are discussed in terms of stereochemical effects on the17O chemical shift of the various oxygen‐containing functionali

ISSN:0749-1581    

DOI:10.1002/mrc.1260321008

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractEvaluation by empirically derived equations for the substituent effect (α, β, γ, δ) on the13C NMR chemical shifts for C‐3, C‐4, C‐5 and halomethyl‐substituent carbon (C‐6) in 5‐halomethyl‐5‐hydroxy‐4,5‐dihydroisoxazoles (where C‐3 substituent=H), alkyl or phenyl, C‐4 substituent=H, alkyl or heteroalkyl and C‐5 substituent (=dior trihalomethyl), taking as reference 5‐trichloromethyl‐5‐hydroxy‐4,5‐dihydroisoxazole, is reported. From the calculated values for the α, β, γ and δ effects for each substituent it was possible to estimate the che

ISSN:0749-1581    

DOI:10.1002/mrc.1260321009

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

Abstract(2‐Ethoxycarbonyl)crotylbromodichlorostannane (1) and (2‐ethoxycarbonyl)allylbromodichlorostannane (2), two compounds with formula RSnCl2Br, were shown by 2D phase‐sensitive EXSY119Sn NMR to undergo halogen exchange, resulting in equilibrium mixtures of RSnCl3, RSnCl2Br, RSnClBr2and RSnBr3. The unidirectional pseudo‐first‐order rate constants were determined by two different methods, the initial rate and the exchange matrix resolution approaches. The data show that the exchange proceeds by single halogen exchange, probably occurring through an intermediate involving two organotin trihalide moieties, as evidenced from the linear dependence of the pseudo‐first‐order rate constants on concentration. The mechanism is brie

ISSN:0749-1581    

DOI:10.1002/mrc.1260321010

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY

摘要:

AbstractRadical anions of alkyl α‐oxocarbothioates and α‐oxocarbodithioates are generated byin situelectroreduction. Their spin density distribution and configuration are discussed in terms of the ESR spectra and semi‐empirical (McLachlan‐type and AM1) MO cal

ISSN:0749-1581    

DOI:10.1002/mrc.1260321011

出版商:John Wiley&Sons, Ltd.    

年代:1994

数据来源: WILEY